For safe operation of railway trains and vehicles on a road, construction gauges beyond which a structure is not allowed to be installed are set with respect to the track or the road. In railway maintenance and inspection work, whether there is no structure within the construction gauge is checked and a distance to the structure approaching the construction gauge is measured. Specifically, position coordinates of the structure near the track are calculated by surveying by a laser scanner and the like or image measurement, and then, a distance from the construction gauge set over the track or a distance falling within the construction gauge is calculated. The obtained distance is represented in a table as a numeric value, and in addition to this, as methods of visual representation, there are a technique of plotting a shape of the construction gauge and a measurement point on the structure in a cross-sectional view of a cross section perpendicular to the track so as to represent (for example, Patent Document 1) and a technique of overlapping a reference region determined by the construction gauge with an object to be imaged within the construction gauge based on an image of a camera so as to display (for example, Patent Document 2).